The worst heat wave in U.S. history came in 1936. The already struggling Midwest was hit hard by extreme temperatures and drought. Crops were destroyed, and more than 5,000 people died. The Midwest and Southwest are currently suffering with drought. While serious, it is not yet a situation like the Dust Bowl.

A
heat wave
is different depending on its location. A region has a heat wave if it has more than five consecutive days of temperatures that are more than 9
o
F (5
o
C) above average. A heat wave in Portland, Oregon might be just an average warm week in Phoenix, Arizona.

Heat waves have increased in frequency and duration in recent years. The summer 2011 North American heat wave brought record temperatures across the Midwestern and Eastern United States. Many states and localities broke records for temperature and for the most days above 100
o
F.

Causes

A high pressure cell sitting over a region with no movement is the likely cause of a heat wave.

What do you think caused the heat wave in the image below (
Figure
below
)? A high pressure zone kept the jet stream farther north than normal for August.

A heat wave over the United States as indicated by heat radiated from the ground. The bright yellow areas are the hottest, and the blue and white are coolest.

Droughts

Droughts
also depend on what is normal for a region. A region that gets significantly less precipitation than normal for an extended period of time is in drought. The Southern United States is experiencing an ongoing and prolonged drought.

Drought has many consequences. When soil loses moisture it may blow away. This happened during the Dust Bowl in the United States in the 1930s. Forests may be lost, dust storms may become common, and wildlife are disturbed. Wildfires become much more common during times of drought.

Summary

A heat wave or a drought is defined as conditions different from normal in a region.

A heat wave is caused when a warm high-pressure cell sits over a region.

Drought may have extremely severe consequences. The severity depends on its duration and intensity.